Respiratory failure can become a life-threatening condition in a few minutes or be the result of a build up over several hours. Respiratory failure is very difficult to predict, and as a result continuous monitoring of respiratory activity is typically necessary in clinical, high-risk situations. Appropriate monitoring equipment used by properly trained clinicians can be life-saving. (see Folke M, Cernerud A, Ekstrom M, Hok B; Critical Review of Non-invasive Respiratory Monitoring in Medical Care; Medical & Biological Engineering & Computing 2003 July; 41(4): 377-383).
Noninvasive patient respiratory monitors are especially useful in situations when drugs having sedative and/or analgesic properties are provided to a patient because these drugs may also reduce the patient's drive to breath and ability to maintain an open airway. Noninvasive respiratory monitors may be used to measure the patient's respiratory rate and exhaled CO2 by analyzing the concentration of the CO2 in the exhaled air. They may also be used to monitor heart rate and saturation of blood oxygen. In other words, noninvasive respiratory monitors are configured to provide multiple indications regarding the physical state of a patient
It is important that a clinician be able to properly analyze all the information provided by a noninvasive respiratory monitor. The American Society of Anesthesiologists emphasizes that, because ventilation and oxygenation are separate physiologic processes, monitoring oxygenation by pulse oximetry is not a substitute for monitoring ventilatory function by capnography. (see Practice guidelines for sedation and analgesia by non-anesthesiologists. American Society of Anesthesiologists Task Force on Sedation and Analgesia by Non-Anesthesiologists. Anesthesiology 2002; 96: 1004-1017). Oxygen saturation usually is maintained, even at a low respiratory rate, so that pulse oximetry might fail to detect respiratory deterioration, particularly if a patient is receiving supplemental oxygen. (see Overdyk F J. PCA presents serious risks. [letter] APSF Newsletter 2005; 20: 33). The use of supplemental oxygen does not correct desaturation due to hypoventilation; it simply delays the progression of respiratory failure from bradypnea to apnea. Thus, even continuous monitoring of heart rate and oxygen saturation (“SpO2”) by pulse oximetry is not a substitute for monitoring end-tidal CO2 (“EtCO2”), respiratory rate, and apneic events by capnography. Capnographic monitoring can anticipate a patient's desaturation by warning of a decrease in respiratory rate and rise in EtCO2. (see Weinger M B. Dangers of postoperative opioids. Anesthesia Patient Safety Foundation newsletter 2006-2007; 21: 61-88). In a procedural sedation study, pulse oximetry identified only 33 percent of those patients with respiratory distress, while capnography captured 100 percent. (see Miner J R, Heegaard W, Plummer D. End-tidal carbon dioxide monitoring during procedural sedation. Acad Emerg Med 2002; 9: 275-280). Therefore, it is important that a clinician be proficient at analyzing all the data that can be obtained from a noninvasive respiratory monitor.
Additionally, there are numerous manufactures of noninvasive respiratory monitors, for example, COSMO by Novametrix Medical Systems, Inc., Wallingford, Conn.; Capnostream by Oridion Capnography, Inc., Bedford, Mass.; POET by Criticare Systems, Inc., Waukesha, Wis., etc. Thus, as will be appreciated from the foregoing, one drawback of using noninvasive respiratory monitors is that significant training may be needed before a clinician can make full use of the information provided by these monitors.
Thus there is a need for a system for generating noninvasive respiratory monitor signals to simulate patient conditions encountered by clinicians in order to train the clinician in the proper use of a particular noninvasive respiratory monitor.